1. Field of the Invention
The present invention relates generally to the field of ophthalmics, more particularly to ophthalmic devices, and still more particularly to ophthalmic devices known as intraocular lenses (IOLs).
2. Background Discussion
At the onset it may be helpful to the understanding of the present invention to define the term "phakic" as it relates to human eyes. The term "phakic" is applied to an eye in which the natural ocular lens is still present. This is in contrast to an aphakic eye from which the natural ocular lens has--for any reason--been removed. A phakic eye is considered a dynamic or active eye because the living natural lens is subject to change over time, while an aphakic eye is considered a static eye because the natural lens has been removed.
Vision in an eye is enabled by light from a viewed image being-refracted to the retina by the cornea and the natural lens (and/or any implanted intraocular lens) located posterior of the cornea.
One relatively common ocular problem is impaired or complete loss of vision due to the natural ocular lens becoming cloudy or opaque--a condition known as cataract. The formation of cataracts is typically associated with natural bodily aging, and most individuals over the age of about 60 years suffer from cataracts at least to some extent.
Cataracts cannot currently be cured, reversed, or even significantly arrested. Accordingly, the corrective action involves surgically removing the natural lens when the lens becomes so cloudy that vision is greatly impaired, the result being that a phakic eye becomes an aphakic eye.
After a defective natural lens has been surgically removed, the current vision-restoring practice (since about the 1940's) is to implant in the aphakic eye an artificial refractive lens called an intraocular lens (IOL) having an optic and optic fixation means. Previously, thick, heavy, high diopter spectacles were prescribed for aphakic eyes. Such spectacles however were and still are generally disliked by most patients for their weight and appearance.
Implantable IOLs were initially constructed from rigid polymethyl methacrylate (PMMA), a hard, biocompatable plastic material. More recently, IOLs have been constructed from a soft, elastically deformable, silicone or acrylate material that enables insertion of the IOLs through small ocular incisions.
In addition to the implanting of IOLs in aphakic eyes to restore vision after removal of the natural lens, considerable interest has recently arisen in implanting IOLs in phakic eyes to correct myopia, hyperopia, presbyopia or astigmatism problems associated with non-cataract natural lenses. This implanting of corrective IOLs in phakic eyes is an often-attractive alternative to the wearing of corrective spectacles or contact lenses, which limit certain activities and even certain professions, or having performed such surgical procedures on the cornea as radial keratomy (RK) or photo-radial keratectomy (PRK), which may not be desired by many individuals for various reasons. The implanting of refractive IOLs in phakic eyes to correct vision problems is considered to constitute one of the remaining frontiers of vision correction.
In an aphakic eye, a replacement IOL is now typically implanted in the posterior chamber of the eye from which the natural lens has been removed. In contrast, a corrective IOL for a phakic eye is most desirably implanted in the anterior chamber of the eye, forwardly of the intact natural lens in the posterior chamber of the eye. The former is called a posterior chamber IOL and the latter is called an anterior chamber IOL, and there are significant construction differences between the two types of IOLs.
With regard to anterior chamber IOLs, there has been renewed interest in IOLs constructed for fixation to the iris (some of the earliest IOLs were iris fixated, anterior chamber IOLs). By fixing the optic supporting structure to the iris itself, contact with the sensitive filtration angle of the eye is avoided.
Iris fixated IOLs are disclosed in U.S. Pat. Nos. 4,215,440 and 5,192,319 to Jan Worst. Both of such patents disclose IOLs employing one or more optic fixation members formed having a pair of pincer arms which, acting together, pinch an anterior surface region of the iris. This pinching action detachably attaches the IOL to the iris so that the IOL optic is ideally fixated in the region of the iris opening (i.e., the pupil of the eye).
However, the present inventor considers that improvements to the iris fixated IOL designs disclosed in the two above-cited Worst patents are desirable and it is a principal objective of the present invention to provide such improvements, particularly in the areas of improving optic centration and enabling small incision implanting.